Citrus Leaves Curling Yellowing Dropping

Q. Hello again! 

I have a puzzling issue happening with a few citrus trees (out of many).  The leaves are curling, yellowing, and ultimately dropping. I attached a few pictures in hopes you could shed some light on the issue. (Any iron deficiencies you see are from trying to extend the time between treatments, something I've been trying to perfect; seems like every 6 weeks is the sweet spot.)

I appreciate any help you can give me, I'd hate to see these trees die! 

Leaf rolling like this on citrus can be a watering problem

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A. If the leaves are rolling or curling into a cigar shape, then this is typically a lack of water. The leaves can turn yellow and drop from the tree if it continues. A lack of water can be from not giving each tree enough water or it can result from not watering frequently enough. 

Strangely, the same can result if you are watering too often but it almost never results from giving a tree too much water in a single application. My suggestion to you, if these trees aren't drip emitters, is to make sure that each tree has at least four drip emitters. 

Replace these emitters with emitters that double the application rate. In other words, if these are 2 gallon per our email letters, replace them with 4 gallon per hour emitters. This allows you to keep the same number of minutes on your irrigation timer and not overwatering other plants on the same valve. 

I would strongly advise you not to use adjustable drip emitters for this purpose. They can be extremely difficult to adjust properly since they seem to act like "whack a mole" when you try to adjust them.

Visit this page from the University of Arizona on citrus problems in the landscape